[ARC5] Lopsided modulation

[Tom Lee]

Yes, the muddle is very odd. Bob said it succinctly and correctly: The 
shape of the modulation spectrum has no impact on symmetry of the 
sidebands. For pure AM or pure FM, you get symmetrical sidebands, 
period. As a professor, I leave it as an exercise to the student to 
compute how high a tank Q would be necessary to produce a pronounced 
asymmetry (hint: you will find it hard to contrive sensible numbers in 
most cases). By far the most common source is the simultaneous 
occurrence of AM and FM. It is difficult to build a 
modulator/transmitter chain that is completely free of incidental 
modulation by the unwanted mode.

Cheers
Tom

-- 
Prof. Thomas H. Lee
Allen Bldg., CIS-205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu
650-725-3383 (public fax; no confidential information, please)

On 2/27/2018 11:05 AM, Richard Knoppow wrote:
> Exactly, this applies to FM, PM and AM. For some reason it seems to be 
> difficult for people to understand. Asymmetry of either AM or FM is 
> usually due to having both.
>
> On 2/27/2018 8:29 AM, Bob kb8tq wrote:
>> Hi
>>
>> In the case of un-equal sidebands, the “symmetry” of the modulation 
>> waveform has
>> no impact.
>>
>> Bob
>>
>>> On Feb 27, 2018, at 11:27 AM, Kenneth G. Gordon 
>>> <kgordon2006 at frontier.com> wrote:
>>>
>>> On 27 Feb 2018 at 16:01, Glen Zook via ARC5 wrote:
>>>
>>>> Now, I admit that I have not really done any experimentation with 
>>>> AM and, as
>>>> such, I cannot definitely say that this asymmetrical voice 
>>>> characteristic can cause
>>>> the same difference with the sidebands as it does with FM. However, 
>>>> my "gut
>>>> feeling" is that it just might be the cause with AM as well as with 
>>>> FM.
>>>
>>> I think one quick way to test this in Neil's case would be to simply 
>>> have his wife, or daughter,
>>> or any handy youngish female, talk into his system while viewing the 
>>> signal with the SDR
>>> receiver.
>>>
>>> Ken W7EKB
>>